1. Field of the Invention
The present invention relates to methods and apparatus for the selective application or deposition of particles to the surface of a substrate or medium therefor. More particularly, the present invention relates to methods and apparatus for controlling and effecting the selective application or deposition of an aerosol or mist of particles, such as magnetic ink particles, to the surface of a substrate or medium therefor for purposes of displaying, printing, copying, and the like, some form of data, information or the like.
2. Description of the Prior Art
Various techniques exist in the prior art for controlling the application or deposition of a cloud or mist of fine particles to a desired surface. Typically, such applications are used for printing, copying, coating, plating, reproducing, and the like. In the main, these techniques involve some form of electrostatic control wherein the particles of the cloud or mist are charged, and the passage of the charged particles to the desired surface is controlled, for example, by selective field deflection or precipitation of the particles out of the path to the intended surface. In other arrangements, selective application or deposition of particles is effected by electrostatic control of apertures leading to the intended surface by blocking or nonblocking fields thereacross.
Typical of the deflection or precipitation-type of electrostatic control is the printing arrangement described by R. E. McCurry et al in their article entitled "Mist Ink Printer" appearing in the IBM Technical Disclosure Bulletin, Vol. 15, No. 8, Jan. 1973. Typical of the blocking/nonblocking field-type electrostatic control of apertures is the printing arrangement described by Pressman in U.S. Pat. Nos. 3,625,604 and 3,694,200, and image reproduction arrangement described by Pressman et al in U.S. pat. No. 3,647,291.
Other techniques for electrostatically controlling the application or deposition of a cloud or mist of fine particles involve creating a latent electrostatic image on an insulating layer or substrate such that particles are selectively attracted and/or repelled in accordance with the polarity of the image. Representative of such arrangements are those described by Hotine in U.S. Pat. No. 3,537,847 and Rank Xerox Limited in British Patent 1,255,568. In Hotine, the electrostatic image is composed of both positive and negative charges while in Rank Xerox single polarity charges are employed.
Although not as widespread as the electrostatic forms of controlling application of fine particles to the surface of a substrate or medium therefor, some forms of magnetic control have been used. Magnetic control generally involves forming a jet or fine spray of magnetic particles and, as with the electrostatic case, deflecting the jet of particles out of the path to the intended surface via a magnetic field. In another scheme, the magnetic particles of the jet are inhibited from reaching the intended surface by using a magnetic field to control emission of the particles from the jet nozzle. Typical of the latter type control is that described by H. E. Hollmann in U.S. Pat. No. 3,925,312 entitled "Magnetic and Electric Ink Oscillograph."
In addition to the above-cited prior art, the following prior art describes, in one form or another, clouds, mists, sprays and the like of ink particles as used in recording, printing, reproducing and the like:
U.s. pat. No. 2,191,827 by R. C. Benner et al for "Apparatus for Applying Liquid to Fabric;" PA1 U.s. pat. No. 2,584,695 by P. J. Good for "Electrostatic Reproduction Process and Apparatus;" PA1 U.s. pat. No. 2,716,826 by W. C. Huebner for "Apparatus for Reproducing Images;" PA1 U.s. pat. No. 3,725,951 by R. E. McCurry for "Electro-Ionic Printing".
One of the major difficulties with the prior art forms of controlling the selective application of particles to the surfaces of a substrate or medium therefor resides in the fact that the selective application is dependent upon significant physical control of the particles so as to effect or impede movement to or away from the substrate or medium. Such physical control introduces aerodynamic problems as well as imposing considerable corona requirements. In addition, the clogging of nozzles and the like, and general contamination are continuing problems. Moreover, because of the amount and intracacy of the control required, the control apparatus is necessarily complex, expensive and difficult to maintain.